Method of forming wire coils



March 20,- 1945.

AMIN

MING

. respective parts.

Patented Mar. 20,1945

METHOD OF FORMING WIRE COILS Harold Caminez, Williamsport, Pa., assignorto Aircraft Screw Products Company, Inc., Long Island City, N. Y., acorporation of New York Application December-'24, 1942, Serial No.470,042 I 3 Claims.

This is a continuation in part of my co-pending application, Serial No.429,023, filed January 31, 1942.

The present invention relates to a method for making wire coils of greatexactness as e. g. coil 5 inserts which have been frequently suggestedfor use in screw connections of a male anda female member, wherein thecoil wire is in engagement with the external and internal threadings ofthe A wire coil of the mentioned type has been described, for instance,in my U. S. Patent No. 2,150,876.

Whereas ordinary coil springs in general re quire only a minor degree ofhomogeneousness and exactness of the dimensions of the wire material ofwhich the coil is made, and also a minor degree of exactness asto theexternal and internal dimensions of the finished article, the wire coilsor inserts of the type here under considera-- tion must have thefeatures of a coil spring and, in addition thereto, must be true to thedesired cross-section and inclination of the wire within unusuallynarrow tolerances. The invention aims, therefore, to provide a methodwhereby a wire coil can be made so as to fulfill the hi rrequirements asfor instance those of an insert for a screw connection. Theserequirements are substantially as follows:

The wire useful for an insert coil must 'be hard but ductile and of goodresiliency. The mate,- rial should be anti-corrosive and must have lowfriction qualitieswith respect to the materials of the members of theconnection for which the insert is destined In certain cases it mustalso be resistant to the attack by the products of coinbu'stionin gasengines- Materials such as a hard bronze and stainless steel have beenfoundparticularlysuited to the purpose. The wire crosssection of theinsert, depending on the. cross-sections of the threads in the femaleand male menibers between which the insert is intended to be used, maybe round oifisquare or it may be one of those cross-sections which haveconverging side portions as for instance, a cross-section of diamondshape or of pear shape as described in my aforementioned Patent No.2,150,876. In the finished insert the wire should be smooth and close--,ly fit the thread grooves of the male and female members. Similarlylocated points of similar cross-sections respectively of an insertshould be equally spaced'from the axisof the insert coil. In particular,if in wire cross-sections as for instance, of diamond or pear shape, aline of sym-' metry of one cross-section coincides with a radius of thecoil, then the lines of symmetry in I other similar cross-sectionsshould also be coincident with corresponding radii. In many instances,the outer diameter of the insert before insertion should be larger thanthe tapped hole so as to provide for adequate spring tension but mustnot be too large so as to render insertion difiicult or even impossible.The coil may have a tang to be gripped by a tool and at least the fronthalf of the first convolution may be undersized to facilitate theinsertion. In many instances, it is also recommended to apply a notchclose to the root of the tang where the latter may be broken offafterthe insertion ofthe coil in a female threaded member.

Now, I have found that it is practically impossible to meet thementioned requirements in an insert coil-wound in the conventionalmanner from wire available on the market if the original wirecross-section is like that desired in the finished insert. In general,the cross-section of the coil wound in the customary manner differs fromthe original shape, and, moreover, different crosssections of the samecoil differ from each other even if taken at the same angle to the coilaxis. Usually there are three major reasons for such happening. First,the wire in its original form is, in general, not suflicientlyhomogeneous as to its material and shape over a length to be coiled.

Second, the wire shipped in the conventional 5 manner, i. e. spooled ondrums or reels ,of not very large diameter, is bent from the start andowing thereto has, what is generally termed a cast,

that means, the particles of the wire which should be arranged, so tosay, in straight lines parallel to the wire axis, actually formlarge-pitched helices. Third, the tension and bending stresses to whichthe wire is subjected during the coiling are not equally distributedover theentire area of the wire cross-section. Every single one of thesecauses is frequently suflicient to interfere with the production of auseful insert. In most instances, however, all three of them act at thesame time'to render a customarily made wirecoil unfit as an insert forscrew connections oi. the type herein considered or for other purposeswhere high precision as to the cross-sectional shape is required.

It will be clear that the least difllcultles are encountered with wireof round cross-section, al-

though even an originally round cross-section will no longer be trulycircular in the finished coil.

Similarly, in most instances, an originally square cross-section will beother than rectangular and in addition thereto. tilted when coiled.Inserts of diamond and pear-shaped cross-sections are among the mostdifilcult ones to produce so as to start from a circular cross-sectionwire. If the be true to the desired dimensions. For this reamaterial isa stainless steel containing, e. g. 18% son, I shall describe the methodaccording to my chromium and 8% nickel, the wire may be first inventionmainly with reference to such shapes. annealed, pickled and then cleanedand provided However, I wish it to be understood that this with an oxidecoating; the cleaning step of operamethod with or without variations ormodiflcation to take place also if the material is a suittions isequally well applicable to wire of other able bronze. Thereafter, theclean wire may be cross-sections, symmetrical or asymmetrical, andreduced in diameter by drawing it through a that the scope of myinvention shall not be limited die preferably of one oi the carbidematerials,

but y he appended claims. 1 as for instance, a die of the material whichis Further objects and details of my invention on the market under thename of Carboloy. will be apparent from the description given here- Thiscold working simultaneously smoothens the inafter and the accompanyingdrawing. surface and increases the homogeneousness of In the drawing:the material'and also the tensile strength, e. g. Figs. 1 to 3 are sideelevation, front and rear from 90,000 p. s. i. in 'the' annealed wire toviews, respectively, of an insert of the type under 150,000 p. s. i. inthe wire of reduced diameter. consideration. Any flaws in the originalwire will also be de- Figs. 4 to 6 are different cross-sections at atected during this step of operation. 5 The regreatly enlarged scale ofa substantially diamondquired size to which the round wire is to bereshaped, a pear-shaped and an asymmetrical wire. duced can beexperimentally determined. The pe tive y. and in each of these figures,the wire may then be provided with another oxide solid lines show thecross-section in the finished coating by heating. This pretreatmentremove insert whereas the dashed lines show the cross- One of theabovementioned causes for faulty'prosection prior to the coiling.duction described in the preceding paragraph.

Fig. 7 is a diagrammatic illustration of a tool Th so-prepared roundwire of stainless steel,

for accomplishing t e Co ing according to the or if the material'is abronze, the wire cleaned invention. and reduced to the required diameterand hav- Referring to the drawing, Figs. 1 to 3' iilusing the desiredqualities may then be shaped by trate an example of the finishedarticle, that suitable means, for instance by drawing it means, aninsert coil 0 of a form which may be through grooved rollers soadjustable that the used in a screw connection between a tapp d wirethickness can be controlled. For measuring boss or nutand an externa lyt d e t o the thickness of a wire of other than circular st'ud. Whereasthe convolutions H of the major or quare cross-section I founda'micrometer portion of the coil are of the same diameter, the usefulwhich has a, lower and an' 'upper anvil.

first convolution I2 is narrower in order to facilieach grooved to matchthe desired shape'of wire.

tate the insertion. A tang I3 is formed at the For the reasonshereinbefore given, the shape front end which can be gripped by aninserting to which the wire is reduced by the last-men- 0 and which isalso useful for holding the Wire tioned drawing operation must bedifi'erent from during the coiling operation as it will be de-- thatrequiredinthe finished insert to compensate scribed hereinafter. -Anotch Il may be profor later changes owing to the coiling. In genvidednear the root of the tang in order to facilieral it can be said that theportion of the crosstate the removal of the latter after the insertionsection above the neutral axis in the bending of the coil. The other end5 of 15116 may be should originally be larger and the portion below cutat a slant with respect to the wire axis to produce a sharp edge' whichmay engage the insert. The difference required depends on varimaterialof the boss 1111i? member, thereby ous factors, particularly on theshape of the wire creasing the resistance of the coil to a forcecross-section,'the diameter of the coil, and also which might tendtoscrew the coilbackward- 0n the wire material. It can be found bycalcula- The wire of the illustrated coil in is of a pear tion but isbetter established by experimentation. shape more clearly shown in Fig.5. However, it Considering, for instance, Fig. 4, it is assumed will beobvious that a coil similar to that illusthat the truncated diamond 20shown in solid trated in Figs. 1 to 3 may as well be made of a lines isthe shape desired in the finished coil. wire having the cross-section ofFig. 4 or of Fig. 6 The diamond has an upper pair of converging or anyother suitable cross-section if so desired, sides 2| and 22 and a lowerpair of converging and that a method applicable for making the coilsides 23 and 24. The border lines of the upper according to Figs. 1 to 3will, in general, be apand lower truncations are denoted by 25 and 20,plicable to wire of any desired cross-section. It respectively, and thehorizontal diagonal by 21. will be further noticed that the pear-shapedThe sides 2| to 24 are of equal length, and the cross-section of Fig. 5is truncated at its top. angles of convergence 20 and 29 are approxi- VFor'other purposes, of course, the wire crossplane, i. e. the diagonal21 in Similarly the diamond cross-section of Fig. 4 is 0 mately 60 inthe illustrated example. It will be truncated .as to its top andlowermost corners. clear that in bending a wire of diamond cross- Thisis done because sharp edges of the consection in a plane comprising thetop and lower volutions are undesirable in a. wire coil insert. mostcorners, the diagonal transversing'that the present case, sections maynclu corner formed y a pair will define the neutral zone. Consequently,when of converging sides. Whether or not such cornere forming the wireinto a, coil, the portion above the are present is immaterial as to theprinciple of diagonal will besubjected to tensile stress causmyinvention, and I shall referJ therefore, hereing a decrease of thecross-sectional area'whereinafter and. inthe appended claims, to such asthe portion below the diagonal will be comcross-sections as, shown inFig. 5 as diamondpressed and the corresponding cross-sectional shapedregardless of whether the cross sectional area will be increased insize. Furthermore, the figure is geometrically a complete diamond or a.ratio of the change in size increases approxitruncated one. matelyaccordingto the distance of a contem- No matter, now, what wirecross-section is .deplated partial area from the neutral zone. Now.sired in the finished coil, I found it advisable to in order to obtain acoiled, i. e. acontlnuouslv that axis should be smaller than in thefinished is necessary to make the sides of the upper tri- 1 ofthe'desire'd cross-section is denoted by 58 to be necessary with regardthereto in view of the When the wire has been provided with thecross-section required to obtain the desired crosstriangles on the samebase, wherein however, the. section of the finished coil,-any cast, ofthe wire upper one has a greater height than the lower occurring ashereinbefore explained, owing to, one, or in other words wherein theangle of con- 5 the original winding of the wire on a drum or vergenceor the upper triangle is smaller than reel of relatively small diameterand/or owing to that of the lower triangle. This is indicated in othercauses for a lack of uniformity, should-be Fig. 4, where the angle 30included by the dotted removed or at least so far removed that the wiretriangle sides 3| and 32 is approximately asmuch will be free from twistover an appreciable length. smaller than the angle 28 as the angle 35init?) Thiscan be accomplished by passing the wire cluded by the sides33 and 34 is greater than through straightening rollers groovedaccording the angle 29. However, I have found that an to itscross-section. The wire so treated may original diamond cross-sectionhaving the sides then be wound on drums or reels of relatively 3| to 34will not always obtain the desired shape very large diameter, thatmeans, a diameter-sevof the diamond 2| to 24 by merely bending or eralhundred times the height of the wire cross-- coiling a so-shaped wire.In most instances it section, to avoid strain on the wire, which is nowready to be worked in the desired insert ll! such, for instance,asillustrated in Figs. 1 to 3. For this purpose, the free end of thewire may be bent wire of diamond cross-section, I provide an originalwire cross-section which consists of two angle very slightly convex asshown at 4| and 42, and the sides of the lower triangle slightly concaveas shown at 43 and 44 in order to form 2 gripped and held straight so asto form the tang I3 shown in Fig. 2; then by rotating the gripped thedesired diamond by bending. Furtherend, the wire may be coiled into theshape the more, it will be seen that the border lines 45 and 6 of thetruncations in the original cross-section insert is intended to takewhen in position beare located above the desired lines and 28, tween thethread grooves of a threaded female respectively, and that they arerespectively long- 25 and a threaded male member. When a length er'andshorter than the latter. It will be clear of wire sufficient for oneinsert has been coiled, that the desired cross-section can be accuratelythe wire'may be cut off at l5. When the torque obtained by bending wireof another original applied to the tang in coiling the wire is releasedcross-section only if extreme care is taken in and the finished insertis also free'in other reselecting the latter according to all prevailingspects, it will spring to an outer diameter larger circumstances in eachinstance, and if the wire than that it had during the coiling. Thislarger is absolutely homogeneous. However, according diameter can beused as a measure in gauging to the foregoing it is. possible toestablish the the insert in respect to both the required dimenoriginalwire cross-section with sufiicient approxsions and the required elasticproperties of the imation to the ideal. material. This is importantbecause the friction In a similar manner the pear-shaped crossof thewire during its insertion in the tapped section 50 of Fig. 5 can beobtained if the wire hole of the member for which it is destined will isoriginally shaped with a cross-section substanbe inadmissibly high'ifthe diameter of the free tially according to the dash line contour. Thiscoil is too large, and the desired wedging action comprises two slightlyconvex sides 5| and 52 0 of the wire between the convolution flanks ofthe converging at an angle 41 somewhat smaller than tapped thread of thefemale member will be too angle 48 of the sides 53 and 54 of thetriangular low if that diameter is undersized. Finally. the upperportion of the cross-section 50. The lower insert may be notchedas at l4near the root of portion 55 of the desired outline in the illustratthetang for the above-stated purpose.

ed example is an arc of a circle. In this case; As stated hereinbefore,according to my inventhe corresponding portion 56 of the original wiretion, an originally selected cross-section of the cross-section is acurve in which the radius of wire is changed during and by" the coilingto the curvature of any point is larger than the radius desired shape,and if the cross-section is orig- .of the are 56. However, the radius ofcurvature inally correctly selected no additional measures of thedeepest, i. e. the middle part of the curve need be applied in order toobtain thedesired' shape. However, in cross-sections such as e. g.illustrated in Figs. 5 to 7,-there is a certain danger sistent with whathas been said with regard to of the wire convolutions tending to tiltunder the the sides 43 and 44 of the lower truncated triangle bendingstresses of the coiling. For this reason, of Fig. 4. If the desiredshape of the lower porit is advisable to guide the wire during thecoiltion of the pear-shaped cross-section is an arc ing so that similarpoints of all wire cross-secof 180, it is of course similar to the lowerportions are correctly and similarly located in relation' of a roundcross-section. Hence, in order tion-to the coil axis. This may beaccomplished to obtain a coil ofcircular cross-section, the-wire byWinding the W e into a rea grOOve he prior to the coiling should have aportion smaller 60 desired pitch and root diameter provided on a than asemi-circle on the one side of a diameter, m d Simultaneously guidingthe Out and another portion larger than a semi-circle on wire portionalon'g stationary flanks which prethe other side "of said diameter; andthe curvature vent the wire from tilting. a of the first mentionedportion should be accord- This method can be still further-improved by56 is shorter than the radii of laterally located points. It will beclear that such a shape is coning to what has been said with respect tothe are as shaping the groove of the mandrel according to the threadgroove of the male member for which the insert is destined, and byguiding" the outer curve .should be larger than the radii of points wireportion in a tapped thread groove of a shape laterally thereof. Fig. 6shofisa wire cross-secaccording to that of a corresponding female tionof asymmetrical shape, wherein the contour member. In other words, thewire may be coiled between two members grooved complementary to at leasta portion of a coil of the desired shape. In this manner, the wire canbe calibrated during the coiling. Moreover, if the grooved manioregoingstatements relating to Figs. 4 and 5. 7d drel and the tool provided witha' t pp d hole 56 in Fig. 5,. whereas in the other portion the radius ofthe curvature of the middle part of the whereas 59 is the circumferenceof the original shape of the wire. No further explanation seems theysmaylbe used to act as dies in the coiling complished in a die the wire willreadily take the section. For instance, if a wire according to Fig.

are of sufliciently hard and resistant material, sible according towhat-has been stated hereinbefore, and, then to coil it on a groovedmandrel in a suitably grooved nut or die member of the type of a drawingtool.

' Although I have hereinbefore described the method according to myinvention mainly as applied to an insert for a screw connection it willbe apparent to those skilled in the art that the -same method is usefulalso in the productionof wire coils for other purposes. Furthermore, it

will be clear that alterations and modifications are possible within theessence and spirit of my invention which, therefore, shall not belimited but by the scope of the appended claims.

I claim:

andsimulta'neously shaping operation. This is of particular advantage,because-it is not always quite "easy to find the correct cross-sectionwhich 8 will transform into the desired shape merelyby coilingthe wire.If, however, the coiling is acdesired shape notwithstanding a slightincorrectness in the selection of the original cross-section, becauseinorder to render the coil form permanent, the wire must any way bestressed beyond its original elastic limit, that means, it must bebrought into a molecular state where it is sufiiciently ductile tosnugly flt the walls of the grooves of the mandrel and tapped die.

Fig. 7 illustrates diagrammatically how the section having two.outwardly converging coiling may be accomplished in the aforesaidstraight-lined sides which comprises the steps of manner. A rotatablemandrel 66 is provided providing the wire to be coiled with across-secwith a slot 6| in its front end. This slot opens tion similarto but difiering from the desired in in a thread groove 62 which isshaped similarly that the angle of the converging sides is smaller tothe inner portion of the desired Wirecross= than desired in the coil andthat the conve in sides are slightly convex in the portion above thatwire axis which is the neutral axis of the crosssection in thesubsequent coiling step, coiling the wire and confining it on all sidesover an appreciable length during the coiling so as to compel .of Fig.4. 0n the contrary, in the present examall points of each wirecross-section to travel on ple it is advisable to continue the flanks ofgroove helical pat s of constant a d qllal D there- 62 to a sharp edge,wherebya certainclearance by insuring symmetrical locations of all wire4 is to be coiled, the groove 62 should have flanks converging at thesame angle as the sides 23 and 24 ot the diamond of that figure. Thebottom of the groove ,need not be according to the line 26 will beprovided for the wire should the latter 1. A method of making a wirecoil of a cross- I be slightly oversized. The mandrel 80 is arranged ina stationary die member 63 provided with a tapped groove 66. Groove 64is shaped according to the sides 2| and 22 ofthe diamond of Fig. 4. Forthe same reason as stated above, groove 64 may have a sharp edge at itsbottom. Grooves 62 and 64 are of equal pitch, and the die may berecessed at 6'5 so that the wire 68 Now it will be clear that the frontend of the wire Bimay be inserted in the slottl when the front end ofthe mandrel is within the die member 63 and the slot is in registry withthe recess 65. By rotating the may be fed through said recess.

mandrel in the sense of the arrow a, the portion of the wire in the rearof its front end can be caused to engage the thread groove 62 of themandrel and simultaneously the thread groove 64 of the die 63 as clearlyshown in the drawing.

Thereby, the wire will be drawn between the walls of said grooves andsimultaneously act as a threading to shift the mandrel axially duringits rotation. Thus, the coil of desired shape and cross-section will beproduced. It will be understood that it has been hereinbefore suggestedto use the die member 63 like a drawing tool. It is also conceivabletoprovide this member 63 with cutting edges as in a conventional die nutin order to do with less accuracy in the selection of the original wirecross-section. However, I 60 have found that such method is lessadvisable because it is extremely diflicult to obtain sumciently smoothsurfaces of thewire if some cutting operation occurs during the coiling.I recommend, therefore, first to make the original wire cross-section ascorrectly as reasonably poscross-sections of the coil with respect tothe axis 01' the latter.

2. A method of making a wire coil of a cross section. having twooutwardly converging as straight-lined sides which comprises the stepsof providing the wire to be coiled with a crosssection similar to butdiffering from the desired. in that the angle of the converging sides issmaller than desired in the coil and that the 'convergso ing sides areslightly convex in the portion above that wire axis which is the neutralaxis of the cross-section in the subsequent coiling step, coiling thewire and simultaneously passing it with said converging sides through adie groove of the desired cross-section.

3. A method of making a wire coil of a crosssection having a pair ofconverging straight-lined sides as the contour of its outer portion andan arc of a convex curve as the contour ofits inner portion, whichcomprises the steps of providing the wire to be coiled with across-section similar to but'diflering from the desired in that theangle -of the converging sides is smaller than desired ously guiding thewire on both converging sides between two straight-lined flanksconverging at the desired angle while guiding the curved portion in agroove of a cross-section according to the desired arc of a curve.

HAROLD cAlvrnmz

